SAN FRANCISCO — Much-needed rain fell on downtown San Francisco and elsewhere in California on Wednesday at the outset of what the parched state hopes is the start to a one-two punch of stormy weather.

The storm was expected to move down the coast, dumping a half-inch to an inch of rain in southern areas late in the day, forecasters said.

A potentially stronger storm moving in late Thursday could bring thunder and dump up to 2 inches of rain in central and southern valleys, 2 to 4 inches in the foothills and up to 6 inches in some mountain spots. State water officials plan Thursday to survey the anemic mountain snow pack, and will likely find that California’s precipitation is badly lagging what’s needed to quench the region’s thirst.

After 2013 ended as the state’s driest year on record, all that predicted rain and snow should be nothing but good news. But there also was a risky side of the downpours.

If the rainfall rate is intense, it could bring flash flooding, “and our ground is so dry ... that we’ll probably get more runoff than we’re absorbing,” said Bonnie Bartling, a National Weather Service weather specialist in Oxnard.

The National Weather Service also noted the potential for mud and debris flows from the burn area of the May 2013 Springs Fire, which scorched nearly 38 square miles of the Santa Monica Mountains as it burned from the edges of suburban homes down to the beach about 50 miles west of downtown Los Angeles.

Numerous other wildfires statewide left scarred landscapes over the past year, including a 400-square-mile area devastated by last summer’s forest fire in and adjacent to Yosemite National Park in the Sierra Nevada.

A so-called Pineapple Express storm brought rain and snow to California earlier this month, and when it departed, the Sierra Nevada snowpack had grown but was still only 29 percent of normal.

“Much of the rain that occurred with the storms early in the month was in the northern half of the state with only very small amounts getting down into the Los Angeles and San Diego area,” Accuweather meteorologist Ken Clark said in an email.

The second of the two storms will bring by far the heaviest of rain to Southern California, he wrote. “In fact as much, or more rain, may fall in parts of Southern California than fall, let’s say, around the (San Francisco) Bay Area when all is said and done.”

Downtown San Francisco is close to its February average of 3.86 inches of rain to date, but it is 11.62 inches below normal for the rain year that began on July 1.

Downtown Los Angeles has recorded only 0.23 inch of rain this month, 3.05 inches below normal to date. The location has received only 1.23 inches since July 1, a deficit of 9.52 inches.